From: Al Viro <viro@zeniv.linux.org.uk>
To: Max Kellermann <max.kellermann@ionos.com>
Cc: linux-fsdevel@vger.kernel.org,
Christian Brauner <brauner@kernel.org>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 20/21] __dentry_kill(): new locking scheme
Date: Mon, 7 Jul 2025 21:31:04 +0100 [thread overview]
Message-ID: <20250707203104.GJ1880847@ZenIV> (raw)
In-Reply-To: <CAKPOu+_q7--Yfoko2F2B1WD=rnq94AduevZD1MeFW+ib94-Pxg@mail.gmail.com>
On Mon, Jul 07, 2025 at 10:00:38PM +0200, Max Kellermann wrote:
> Sorry Al, I don't get it.
> I understand that objects that are still referenced must not be freed,
> and of course a dentry that has started the process of dying by
> __dentry_kill() needs to remain in the tree, and that its parent must
> not be freed either. Of course!
>
> But none of this explains why you added this "d_lockref.count<0"
> check, which I doubt is correct because it causes a busy loop, burning
> CPU cycles without doing anything.
Busy loop here means that everything in the tree is either busy or already
in process of being torn down *by* *another* *thread*. And that's already
in process - not just selected for it (see collect2 in the same loop).
What *can* we do in that case? On the level of shrink_dcache_parent(), that
is. Ignore that these suckers are there? Fine, but that means we are failing
to evict the stuff that has no busy descendents.
The interesting question is what the other thread is doing...
next prev parent reply other threads:[~2025-07-07 20:31 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-24 6:02 [RFC][PATCHSET v3] simplifying fast_dput(), dentry_kill() et.al Al Viro
2023-11-24 6:04 ` [PATCH v3 01/21] switch nfsd_client_rmdir() to use of simple_recursive_removal() Al Viro
2023-11-24 6:04 ` [PATCH v3 02/21] coda_flag_children(): cope with dentries turning negative Al Viro
2023-11-24 21:22 ` Linus Torvalds
2023-11-24 22:58 ` Paul E. McKenney
2023-11-24 6:04 ` [PATCH v3 03/21] dentry: switch the lists of children to hlist Al Viro
2023-11-24 7:44 ` Amir Goldstein
2023-11-24 7:55 ` Al Viro
2023-11-24 8:02 ` Amir Goldstein
2023-11-24 6:04 ` [PATCH v3 04/21] centralize killing dentry from shrink list Al Viro
2023-11-24 6:04 ` [PATCH v3 05/21] shrink_dentry_list(): no need to check that dentry refcount is marked dead Al Viro
2023-11-24 6:04 ` [PATCH v3 06/21] fast_dput(): having ->d_delete() is not reason to delay refcount decrement Al Viro
2023-11-24 6:04 ` [PATCH v3 07/21] fast_dput(): handle underflows gracefully Al Viro
2023-11-24 6:04 ` [PATCH v3 08/21] fast_dput(): new rules for refcount Al Viro
2023-11-24 6:04 ` [PATCH v3 09/21] __dput_to_list(): do decrement of refcount in the callers Al Viro
2023-11-24 6:04 ` [PATCH v3 10/21] make retain_dentry() neutral with respect to refcounting Al Viro
2023-11-24 6:04 ` [PATCH v3 11/21] __dentry_kill(): get consistent rules for victim's refcount Al Viro
2023-11-24 6:04 ` [PATCH v3 12/21] dentry_kill(): don't bother with retain_dentry() on slow path Al Viro
2023-11-24 6:04 ` [PATCH v3 13/21] Call retain_dentry() with refcount 0 Al Viro
2023-11-24 6:04 ` [PATCH v3 14/21] fold the call of retain_dentry() into fast_dput() Al Viro
2023-11-24 6:04 ` [PATCH v3 15/21] don't try to cut corners in shrink_lock_dentry() Al Viro
2023-11-24 6:04 ` [PATCH v3 16/21] fold dentry_kill() into dput() Al Viro
2023-11-24 6:04 ` [PATCH v3 17/21] to_shrink_list(): call only if refcount is 0 Al Viro
2023-11-24 6:04 ` [PATCH v3 18/21] switch select_collect{,2}() to use of to_shrink_list() Al Viro
2023-11-24 6:04 ` [PATCH v3 19/21] d_prune_aliases(): use a shrink list Al Viro
2023-11-24 6:04 ` [PATCH v3 20/21] __dentry_kill(): new locking scheme Al Viro
2025-07-07 17:20 ` Max Kellermann
2025-07-07 17:29 ` Al Viro
2025-07-07 17:43 ` Max Kellermann
2025-07-07 18:00 ` Al Viro
2025-07-07 18:11 ` Max Kellermann
2025-07-07 19:31 ` Al Viro
2025-07-07 20:00 ` Max Kellermann
2025-07-07 20:31 ` Al Viro [this message]
2025-07-07 20:39 ` Max Kellermann
2025-07-07 20:49 ` Al Viro
2025-07-07 20:52 ` Max Kellermann
2025-07-07 20:59 ` Al Viro
2025-07-07 21:06 ` Max Kellermann
2025-07-07 21:32 ` Al Viro
2025-07-07 21:47 ` Max Kellermann
2025-07-07 22:19 ` Al Viro
2025-07-07 22:37 ` Al Viro
2025-07-08 4:45 ` Max Kellermann
2026-01-21 21:55 ` Al Viro
2026-01-22 6:24 ` Al Viro
2025-07-07 22:26 ` Al Viro
2023-11-24 6:04 ` [PATCH v3 21/21] retain_dentry(): introduce a trimmed-down lockless variant Al Viro
2023-11-24 21:28 ` [RFC][PATCHSET v3] simplifying fast_dput(), dentry_kill() et.al Linus Torvalds
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20250707203104.GJ1880847@ZenIV \
--to=viro@zeniv.linux.org.uk \
--cc=brauner@kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=max.kellermann@ionos.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox